1. Field
The aspects of the disclosed embodiments relate to a radiation guide for a radiation detector, and a scattered radiation detector.
2. Brief Description of Related Developments
Scattered light detectors may for example be smoke detectors. Such detectors comprise a radiation source, for example an LED (light emitting diode), and a radiation sensor sensitive for the emitted radiation. The two components are in one embodiment arranged such that the sensor is prevented from receiving direct radiation from the source. Rather, radiation received by the sensor would be radiation scattered by particles, for example smoke particles, in the ambient atmosphere. The disadvantage of the known scattered light sensors is that either sensitivity is poor because both on the side of the radiation emitting device and on the side of the sensing device the numerical aperture is small so that the signal is weak, or if a large aperture is desired, the device becomes voluminous.
Another disadvantage is that light from the optical emitter scattered from parts of the smoke detector itself can be received by the detector and leads to an offset that might vary due to surface contamination and ageing. Such variable offset increased the detection threshold for smoke to be detected.
Another technology for detecting smoke in the atmosphere (or generally: scattering particles in an ambient fluid) is to establish a direct line of sight between a radiation source and a sensor (which may also include mirrors), and using the effect that scattered-out intensity reduces the signal sensed by the sensor. In these sensors, the detection signal is weaker than the non-detection signal. For increasing sensitivity, a long optical path is desired for achieving a larger accumulated intensity-weakening effect by a given particle concentration. Such optical paths may be lengthened by providing folded paths, e.g. a pentagram-like path using mirrors. This again leads to a comparatively bulky device.
Known prior art documents for the addressed technology are U.S. Pat. Nos. 6,778,091 B2, 6,756,906 B2, GB 2 389 176 A, U.S. 2001/0038338 A1, U.S. Pat. No. 6,107,925, GB 2 342 987 A, U.S. Pat. No. 5,821,866, GB 2 314 618 A and EP 0 588 232 B1.